Humankind has used, studied and developed fragrances from ancient times. As early as 4,00 B.C., fragrant substances were burned in China, Arabia and Egypt. Thus, the term “perfume” derives from the Latin phrase “per fumum” meaning “through smoke”. Although perfume in the modern cosmetic sense of an alcohol-based solution did not exist in ancient times, evidence of the practice of fumigation with incense combining wood, spice, fruit or resin with a heat source has been found in the hieroglyphics discovered at Edfou and Philae. In his works “Canon Medicinae” and “Treatise About the South” Avicenna (880-1037 A.D.), the physician and mystic mentioned many aromatic resins, such as frankincense, storax, galbanum, ambergris, asant and myrrh, all noted for their healing properties.
While the first alcohol-based perfume was developed for Queen Elizabeth of Hungary in 1370, modern perfumery is considered to have begun in 1806 with the marketing of Eau de Cologne by Jean Maria Farina. His formula consisted of an alcohol-water base scented with an oil composed of neroli, bergamot, rosemary and lemon. The building blocks of all fragrances are the essential oils extracted from flowers, grasses, seeds, leaves, roots, barks, fruits, mosses and resins. Important advancement in fragrances commenced in the nineteenth century with the emergence of organic chemistry, allowing investigators to isolate fragrant molecules and reproduce them synthetically. Synthetics (aroma chemicals) have enabled the replication of scents from flowers, like lilac and lily of the valley that cannot be captured any other way. Fragrance in its most basic form is a molecular composition of carbon, oxygen, hydrogen, nitrogen, and sulphur. When exposed to light or heat that chemical structure can deteriorate.
In the nineteenth century perfumer or “nose” Septimus Piésse implemented a classification system for perfume which remains today. That system corresponds to the musical scale wherein a fragrance composition contains individual notes or essences. The term “notes” can refer to a single ingredient such as jasmine, frankincense or lemon, but may also refer to a perfume's phase or a fragrant blend of ingredients that combine to give a fragrance its top, middle, or base notes. The term “common thread” describes a perfume's ability to flow from one phase to another in a cohesive rather than a discordant fashion. A perfumes “octave” refers to the height of a particular odor or ingredient as it makes it presence known during the drydown process. In 1923, Poucher added to the work of Piésse in publishing a classification method looking to a fragrant ingredient's evaporation rate based upon an overall scale of 1 to 100. In the modern day a perfumer may compose from a repertoire of over 2000 notes. The Société francaise des Parfumeurs has published a perfume classification listing: the citrus family; the floral family; the fern family; the chypre family; the woody family; the oriental family; and the leather family.
The olfactory reaction to a perfume is to its vapor. When encountering the nose, the vapor is warmed, humidified and channeled to the olfactory epithelium. The olfactory sensory cells have cilia with receptor sites that capture and bind the vapor molecules. How those vapor molecules are translated by the receptors into a smell remains a matter of conjecture. Recently, a vibrational theory has arisen wherein the molecules comprising the scent vapors vibrate and switch on the receptors which, in turn, communicate with the limbic system, the seat of emotion and memory in the brain.
See generally:                Newman, “Perfume, The Art and Science of Scent”, National Geographic Society, Washington, D.C., 1998.        Booth, “Perfumes, Splashes & Colognes”, Storey Publishing, Pownal, Vt., 1997.        Fischer-Rizzi, “The Complete Incense Book”, Sterling Publishing Company, New York, N.Y. 1996.        Pavia, “The World of Perfume”, Knickerbocker Press, New York, N.Y., 1995.        
The present day fragrancing industry maintains two general endeavors, one being personal or cosmetic perfumes typically marketed in artistic containers, and fragrances combined with living space emission devices. The latter devices include incense burners, candles, oil warmers and generally three categories of continuous action fluid dispensers. One of those three categories involves the utilization of a wick which protrudes from a bottle. The wick can be of various diameters or heights. This wick can also be heated using, generally, a resistor in a ceramic housing, the heating of the wick tending to enhance the drawing of fragrance liquid from some reservoir. The second device is one employing a nebulizer with an atomized particle size discriminator function. A third uses a spray nozzle similar to ones employed by an aerosol or a cologne spray with an automated/timed plunger that depresses the spray nozzle periodically, thereby atomizing the liquid. The atomized particles of the fragrance fluid can be observed emanating from a nozzle and thus vaporize into the atmosphere from that condition. With any of the emanating device approaches the liquid fragrance involved may be combined with a solvent to weigh down or dilute the fragrance in order to decrease the evaporation characteristics. In general that solvent is a glycol with an emulsifier, for example, a glycol ether marketed under the trade designation “DOWANOL”. Typically, the fragrance is combined in a 1:1 ratio with a solvent, an arrangement adding to the cost of the fragrance formulation. While the heated wick based devices are inexpensive, as noted above, the heating of fragrances may be deleterious. On the other hand, the nebulizing devices can be comparatively expensive. For either approach, typically a duty cycle is involved in device operation to avoid overwhelming the living space with fragrance vapor.